Process of making tap-blanks.



PATENTED SEPT. 1, 1903.

F. N. GARDNER.

PROCESS OF-MAKING TAP BLANKS.

flederw/afardlzer ZM/(mHw J UNITED STATES iatented September 1, 1903.

PATENT OFFICE.

FREDERICK N. GARDNER, OF BELOIT, WISCONSIN, ASSIGNOR TO CHARLES H.BESLY, OF CHICAGO, ILLINOIS.

PROCESS OF MAKING TAP-BLANKS.

SPECIFICATION forming part of Letters Patent No. 737,833, datedSeptember 1, 1903. Application filed December 19 1900. Serial No.40,379. p imena) To (064 w/tom it may concern.-

Be it known that I, FREDERICK N. GARD- NER, of Beloit, in the county ofRock and State of Wisconsin, haveinvented certain new and usefulImprovements in Processes of Making Tap-Blanks; and I do hereby declarethat the following is a full, clear, and exact description thereof,reference being had to the accompanying drawings, and t0 the letters ofreference marked thereon, which form a part of this specification.

This invention relates to a novel method of manufacturing blanks forscrew-taps of that class provided with a plurality of symmetrically andlongitudinally disposed lands separated by a like number ofclearance-grooves, said lands being adapted to be provided on theirouter faces with cutting-teeth to produce the finished product.Screw-taps of this character are usually provided with four raised landsand four clearance-grooves, and it has been the common practice inmanufacturing such taps to first reduce, by means of a propercutting-tool, the rod or blank from which the tap is made to therequired diameter to form the shank of the finished tap, thereafterforming a spiral V-shaped thread on the enlarged part of the blank bymeans of a milling-tool or otherwise, and finally cutting away the blankin the part on which said thread is formed to provide longitudinalclearance-grooves and between the grooves raised lands, the outer facesof which are provided with cutting-teeth. One of the chief objections tothe method thus outlined for making screw-taps is the great waste of themetal growing out of the reduction or cutting down of the end of theblank to form the shank and the cutting away of the metal to form theclearance-grooves. As these taps are made from a fine quality oftool-steel, the method heretofore practiced is an unduly expensive one,both by reason of the quality of steel used and the amount of laborrequired in shaping the taps.

One of the principal objects of the present invention is to produceblanks for screw-taps of the character set forth without the wastefuluse of the material from which said taps are made, and thereby diminishthe cost of the finished product. A further object of the invention andlooking also toward the economy in the manufacturing of said blanks isto provide a process whereby the blanks may be made with a lessexpenditure of time than by the processes heretofore practiced.

In manufacturing screw-taps in accordance with my novel process Iproceed generally as follows: The blank is made from a rod or blank of auniform diameter equal to that of the shank of the finished tap andabout the length of said finished tap. The rod is first heated at theend thereof on which the cutting-teeth are afterward formed to bring thesame to a forging heat and to make the metal so soft that it will easilyflow under pressure, and said rod is thereafter subjected to thepressure of a series of radially-movable dies acting to displacelaterally and radially outward the metal of the rod to form thereon aplurality of longitudinal grooves and between said grooves elevatedlongitudinal ribs or lands. After said grooves and elevated lands havebeen thus formed and the blank thereby finished said lands are cut bymeans of the usual milling-tool or otherwise to form cutting-teeththereon, said teeth being spirally disposed, so as to form spiralscrewthreads. Either before or after the cutting teeth have been formedthe outer end of the tool is tapered, if it be a taper or plug tap. Theouter end of the shank is also given suitable angular form to enable thesame to be engaged with a stock or other actuating implement. I Theradial inward pressure of the dies against the blank to form theclearance grooves therein causes the metal of the blank to be shiftedlaterally and radially outward and to little or no extent endwise, sothat the lands or ribs on which the threads are formed after the swagingof the blank has been completed extend outside the circumference of theshank, thereby giving to the cutting end of the tool the requiredincrease of diameter over the shank thereof.

The longitudinal grooves between the lands of the tap are formed by theoperation of two or more sets of dies having different widths of workingfaces, the set used in the initial step of the swaging process havingrelatively thin edges, which act along narrow longitudinal lines of theblank and form narrow inithat the work of the succeeding steps is onlyto widen the grooves. By this means I am enabled to form the groovesWithout appreciably elongating the blank, so that practically all of theshifting of the metal due to the swaging process is lateral, it beingobvious that the initial set having narrow working faces may be forcedinto the blank without tendency to elongate the same and that the effectof the other dies is to widen the grooves and shift the metal of theblank radially outward or laterally rather than shift the samelongitudinally.

I have illustrated in the drawings the several steps employed in thepractice of my novel process to form a screw-tap of that kind known as aplug tap, the appearance of the blank in the several stages of theprocess and of the finished tap, and have also illustrated the dies bywhich the clearancegrooves are formed.

In said drawings, Figure 1 is a view of a plain cylindric blank or rodfrom which the screw-taps are made. Fig. 2 is a view of said blank afterthe clearance-grooves have been formed therein by the swaging processdescribed and before the screw-threads have been cut on the lands. Fig;3 is a side elevation of the completed tap. Fig. 4 is an axial sectionthereof. Figs. 5 and 6 are cross-sections on lines 5 5 and 6 6 of Figs.2 and 3, respectively. Fig. 7 is a side elevation of one of the dies.Figs. 8 and 9 are transverse sections of said die, taken on lines 8 8and 9 9, respectively, of Fig. '7. Figs. 10, 11, and 12 illustrate intransverse sections the different steps or stages of forming the grooveswhen the-grooves are formed by the combined work of three different setsof dies.

As shown in the drawings, A indicates a plain cylindric blank or rodfrom which a tap is to be made, the diameter of said blank being equalto the diameter of the shank A of the completed tap. B designates one ofthe dies by which the longitudinal clearancegrooves located between thecutting-lands are formed. Fig. 2 illustrates a blank after the dies havebeen applied thereto to form in the sides of the blank longitudinalgrooves a, between which grooves are located the lands 0,, 'upon theouter faces of which are formed the cutting-teeth of the completed tap.The clearance-grooves a may be formed in any suitable manner-as, forinstance, by the use of a machine constructed for that purpose andillustrated in a prior United States Letters Patent granted to myselfand A. Benja: min Oadman on the Sthday of October, 1901, No. 684,216,said machine consisting generally of a set of radially-movable dieswhich have sliding engagement with a suitable head or support and areadapted to be moved radially inwardly and outwardly toward and from theblank in such manner as to effect equal and simultaneous pressure onsaid blank, which is placed and held centrally between said dies inproper position for contact therewith of said dies. Before the blank issubjected to the swaging operation it is heated to the propertemperature to enable the grooves or depressions to be formed therein bya single operation of the set of swagingdies to be used thereon.

The working faces of the dies are preferably so formed as to make deeperdepressions in the ends of the grooves adjacent to the shank than at theouter ends thereof, said dies for this purpose having their workingfaces inclined from one end thereof to the other, as plainlyindicated inFig. 7. The ends of the dies which form the inner ends of the grooves (tare rounded, as indicated at b, to make the grooves gradually shalloweruntil they merge into the cylindric surface of the shank. Moreover,inasmuch as the outer ends of the lands a. in the completed die aretapered, as indicated at a in Figs. 3 and 4, the curvature of the outerends of the work- 'ing faces of the dies are flatter than the inner endsof said working faces, as will be clearly understood from a comparisonof Figs. 8 and 9, it being obvious that less metal needs to be shiftedoutwardly at the outer end of the tool than in the intermediate parts ofthe cutting-surface thereof.

In order to prevent an appreciable elongation of the blank under thepressure of the swaging-dies, (it being desirable that the shifting ofthe metal due to the pressure of the swaging process be lateral andradial instead of longitudinal,) the said grooves are formed by thecombined action of two or more sets of dies, the initial set of dieshaving comparatively narrow working faces and the'working faces of thedies which follow having grad-ually wider faces until the last set, thework ing faces of which are made to correspond to the contour desiredfor the finished groove.

As herein shown, the clearance-grooves a are formed by three separatesets of dies B, and the manner of using said dies is shown in Figs. 10,11, and 12. A set of dies for the initial operation is shown in Fig. 10,wherein it will be seen the working faces of the die are much narrowerthan the completed grooves. The initial set of dies are, however, forcedinto the blank to a depth equal, or nearly so, to the full depth of thegrooves in the completed tap. The second set of dies are show-n in Fig.11 and are provided with wider working faces than the initial set, butof less width than the final set.

Said dies enter the par 737,833 I as tially-formed groove made by theinitial set of dies and act as they enter said grooves to shift themetal of the blank laterally and radially outwardly. The third or finalset of dies, when the swaging process is a threestage one, is shown inFig. 12, and the working faces thereof are made ofa width to correspondto the final contour of the grooves and act to complete the grooves. Bythis method of forming the grooves the shifting of the metal in theswaging process is almost wholly lateral and radial, whereas if thegrooves were formed at once by a single set of dies whose working faceswere of the contour and size of the finished grooves it would be obviousthat said dies would produce an appreciable and objectionable elongationof the blank. Moreover, if such grooves be formed at one operationgreater power would be required to force the dies to their Work andgreater strain would be brought upon the machine for effecting theswaging.

After the grooves have been formed in the manner described the outerfaces of the lands a are cut to form thereon spirally-arrangedcutting-teeth a, said teeth being formed by the action of'the usualmilling-tool or otherwise, as found most convenient or desirable. Afteror before the teeth are so formed the outer ends of the lands are out orground away to taper the same, as shown in Figs. 3 and 4, to provide forthe proper entry of the tap into the hole tobe threaded.- The inner endsof said lands are also preferably cut away to remove the portion a(shown in Fig.

2) and extending from the cylindric part of the shank to the adjacentcutting-teeth, as shown in Figs. 3 and 4, said cutting-teeth terminatingat or about the point where the grooves begin to grow shallow. The outerend of the shank is thereafter squared or provided with flat faces, ifdesired, to provide proper engagement therewith of a stock or the like.The tap is now ready for use so far as its construction is concerned. Asa matter of finish, however, the bottom of the grooves a will desirablybe smoothed by the action of an emery-wheel or the like.

I claim as my invention The hot swaging process of making screwtapblanks from cylindric rods, which consists in first applying radialpressure to the heated blank along narrow longitudinal lines to displacethe metal of the blank laterally without materially elongating the sameand to form deep and narrow, symmetrically arranged, longitudinalgrooves, and subsequently by lateral pressure on the sides of saidgrooves, further displacing the metal of the blank laterally andradially outward to widen the grooves, and bring the blank to thedesired shape.

In testimony that I claim the foregoing as my invention I aifix mysignature,in presence of two witnesses, this 8th day of December, A. D.1900.

. FREDERICK N. GARDNER. Witnesses:

JNO. 0. R001), F. S. THACKER.

